|Publication number||US8160630 B2|
|Application number||US 12/008,173|
|Publication date||Apr 17, 2012|
|Filing date||Jan 8, 2008|
|Priority date||Oct 20, 1999|
|Also published as||CA2387167A1, CA2387167C, CN1154255C, CN1391732A, DE60035703D1, DE60035703T2, EP1224746A1, EP1224746B1, US20080108315, WO2001029985A1|
|Publication number||008173, 12008173, US 8160630 B2, US 8160630B2, US-B2-8160630, US8160630 B2, US8160630B2|
|Original Assignee||Nokia Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (20), Classifications (10)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation of U.S. patent application Ser. No. 10/110,867, filed on Jul. 10, 2002 now abandoned, and claims benefit thereof under 35 U.S.C. §120.
The invention relates to transmission power control in a mobile communications system. In particular the invention relates to power control in a CDMA system
Transmission power control is used in order to achieve optimum transmission power at which data can be conveyed in the desired manner to the recipient. The aim is to realize error-free data transfer at sufficient transmission power, however without using excessive transmission power which consumes electric energy at the transmitting device and causes interference with other radio connections.
As is known, the adequacy of transmission power is measured as a ratio of signals to interferences at the receiving end. A common ratio is the so-called SIR (Signal to Interference Ratio) value indicating the ratio of signal power to the interference power. Another ratio which is used is the CIR (Carrier to Interference Ratio) value describing the ratio of carrier wave power to the interference power. In radio systems a target level is typically specified for the transmission power at the receiving end. Advantageously in each radio connection the transmission power is set such that the target level is just achieved. Because of the reasons mentioned above it is disadvantageous to set the transmission power higher than the target level. The target level may advantageously be specified as a range in which the transmission power is sufficient in order to transfer the information to the recipient without errors.
In prior-art solutions a target level or range is specified for the SIR value. This target level is a parameter transferred along with messages when negotiating on a bearer. A bearer refers here to the entity comprised of all the factors that are involved in the data transfer between a base station and a given terminal. The bearer concept includes, among other things, the data transfer rate, delay, bit error ratio and the variations in these within certain minimum and maximum values. One can think of the bearer as a data transfer path which is a produce of all these factors and which links a base station with a given terminal, providing a way to transfer payload data therebetween. One bearer typically, especially in modern systems, links one terminal with one base station. Multimode terminals may have several simultaneous bearers linking them with one base station. If the system is capable of macrodiversity combination the bearer(s) may link a terminal and a network through more than one base station simultaneously.
The problem associated with the arrangement according to the prior art may be illustrated through the following example. Let us assume that in the arrangement according to the example a terminal needs on average a SIR value of 15 dB in order to achieve a connection quality which is good enough, and that the terminal can achieve that SIR value. Let us further assume that the operating range of the SIR estimator 11 is from 0 to 14 dB, for instance. Initially, the SIR value given by the SIR estimator 11 and power control element PC_1 12 is set to 13 dB. Then, however, the quality of the connection is not good enough for data transfer. The quality loop 15 detects errors in the signal and instructs to increase the SIR value. In the exemplary prior-art solution the SIR value is increased in steps of 0.5 dB. As the maximum value of the SIR estimator is 14 dB and the SIR target level given by the quality loop 15 is higher than the said 14 dB, the transmission power is increased. At the same time the SIR target level is raised whereby the transmission power further increases. A certain transmission power value, which is high enough, produces a connection quality good enough, whereby the quality loop 15 starts to drop the SIR target level. The SIR target level is dropped in steps considerably smaller than those used to raise it, so that the transmission power increases as long as the SIR target level is smaller than the SIR value given by the SIR estimator. When the transmission power has increased too much, the connection in question interferes with other possible connections.
Let us consider another problem relating to the arrangement according to the prior art. A problematic situation may arise e.g. when the terminal is already transmitting at maximum power even though the SIR value given by the SIR estimator and the real SIR value are smaller than what would be required for sufficient quality. Thereby, the quality loop attempts to further raise the SIR target level still higher when in fact sufficient quality will never be achieved since the transmission power already is at its maximum. When the terminal e.g. moves on to such a geographical area where it achieves sufficient connection quality at a lower transmission power, the transmission power decreases slowly since the SIR target level given by the quality loop 15 has risen very high, coming down very slowly. Thus the terminal unnecessarily transmits at excessive power. Such a situation may arise e.g. as a result of a so-called corner effect. A corner effect means a rapid improvement of connection quality especially in urban areas. For example, on the different sides of one and the same block the connection quality may vary by up to tens of decibels. Then, in a situation where the transmission power on a first side of the block has risen to the maximum value the SIR target level of the said quality loop has been raised rather high. Moving on to the corner of the same block and further to a second side, where the connection quality is considerably improved, the transmission power stays high for a long time still because the quality loop 15 drops the SIR target level very slowly. A similar problem may arise in other similar situations in which the quality of the connection may vary considerably.
An object of this invention is to eliminate the above-described disadvantages of the prior art.
The objects of the invention are achieved by setting an operating range for the said quality loop, which prevents excessive increase of transmission power.
The method according to the invention for controlling transmission power in a telecommunications system comprising at least one terminal and at least one network element and arranged so as to include at least a power control element and means for determining a value representing the quality of a signal is characterized in that
The arrangement according to the invention for controlling transmission power, which arrangement comprises a power control element, is characterized in that the arrangement further comprises
The network element according to the invention, which comprises a transmission power controller, is characterized in that the network element further comprises
Other advantageous embodiments of the invention are specified in the dependent claims.
According to the invention limits are set for the target values, such as the SIR values, representing the quality of a signal, which limits define a reference range by means of which excessive increase of the transmission power can be prevented. Advantageously the limit for a first target value of the quality loop is arranged to be the same as a first limit output by the measuring element measuring the quality of the signal. A second target value may also be set for the quality loop, arranged to be the same or a little lower than a second limit output by the measuring element measuring the quality of the signal.
The invention is below described more closely, referring to the attached drawings in which
Like elements in the figures are denoted by like reference designators.
Let us next consider an arrangement realizing an arrangement for preventing excessive increase of transmission power. This is achieved by arranging the value representing the quality of the signal so as to have either an upper limit or a lower limit or both in order to limit the transmission power.
In an arrangement according to the invention the quality of the received signal is measured by a measuring element which gives to a first power control element a value representing the quality of the signal. The arrangement according to the invention further comprises a quality loop for measuring errors occurring in the received signal by means of an error checking means which controls a second power control element. The second power control element gives a target value for the value representing the quality of the signal which target value is compared in a comparing element. In the comparing element it is ensured that the target value stays within a reference range defined by predetermined limit values. From the comparing element the target value is given to the first power control element where the value representing the quality of the signal, given from the said measuring element, is also compared with the target value, and based on the comparison, the transmission power is adjusted. The said value representing the quality of the signal may be e.g. a SIR value, CIR value or any other similar value. In the following, we will be considering situations in which the value representing the quality of the signal is a SIR value. Furthermore, in the examples to follow the said measuring element is a SIR estimator arranged so as to at least measure the quality of a received signal and to output a corresponding characteristic. Here, the characteristic the SIR. It is obvious to a person skilled in the art that the selected values and the said elements may be other than those mentioned above as long as they can realize the corresponding functions.
It is obvious to a person skilled in the art that the above-described comparing element according to the invention comprises a first means 41 which ensures that the said target level for the value representing the quality of a signal is in accordance with the limits of the predetermined reference range, as described above, and a second means 42 in order to give the final target level, for the value representing the quality of the signal to the power control element 12.
We may study the operation of the arrangement according to the invention by examining the signal diagram shown in
Let us next consider with the help of
It is obvious to a person skilled in the art that the limit values for the said SIR value can be set as desired. The object, however, is that certain values will be defined for the SIR value estimation and for the maximum and minimum values of the quality loop by means of standardization, for example. Thus it can be ensured that the quality can be kept sufficient everywhere for connections of different operators. Standardization is particularly advantageous in an, arrangement where the comparison between the SIR value given by the quality loop and the SIR estimation range is arranged so as to be realized in a radio network controller (RNC) of a third-generation mobile communications network. According to the invention it is also possible to arrange for the SIR value only to have one limit value specified for it.
The power control arrangement according to the invention may be applied in a terminal, such as e.g. a mobile station, which utilizes a radio network in its connections. The power control arrangement, according to, the invention may be realized e.g. in the transmitter and receiver units of a mobile station, or the like.
According to another arrangement, the power control function may be realized in a base station BS. The arrangement according to the invention may then be realized e.g. in such a manner that measurements are carried out in the area of a given base station to ensure that the SIR value can be good enough in a certain area. The base station may be adapted so as to include an arrangement according to the invention which comprises the same or corresponding means as those described above. It is particularly advantageous to realize the arrangement in the transmitter and receiver units of the base station similarly as in the above-described case of the mobile station.
According to a third advantageous arrangement the comparison may be realized in a radio network controller RNC so that base station specific parameters used by the radio network controller specify the above-mentioned reference range for limiting the value representing the quality of the signal. Such an arrangement may also be realized in such a manner that the radio network controller RNC gives to the base stations the operating ranges for the means determining the value representing the quality of the signal and, if necessary, adjusts them e.g. in a situation where the said reference range differs from the said operating range. Advantageously the operating range and reference range data are stored in the radio network controller.
It is obvious to a person skilled in the art that a network element according to the invention which comprises a transmission power controller is adapted so as to include, in accordance with the invention, a first means for determining a reference range for a value representing the quality of a signal, a second means for determining a first target level for the value representing the quality of a signal, and a comparing element for limiting the said first target level for the value representing the quality of a signal to the said reference range in order to determine a final target level for the value representing the quality of a signal. A network element according to the invention may also comprise other means depending on the operation of the network element in question.
It is obvious to a person skilled in the art that the corresponding arrangement may also be realized in any network element in which functions related to power control may be performed. It is further obvious that the implementation of the method according to the invention may be divided between a plurality of network elements.
The arrangement according to the invention may be used e.g. in mobile communications networks to control the transmission power in order to reduce interference in the network. Advantageously the arrangement according to the invention finds utility e.g. in third-generation mobile communications networks, such as UMTS, in which wideband CDMA (WCDMA) technology is used in data transfer. Apart from mobile systems the arrangement according to the invention may also be used in other telecommunications systems where similar power control is performed.
It is obvious to a person skilled in the art that the arrangement according to the invention may be applied to other radio networks in which the transmission power is adjustable. The arrangement according to the invention which was presented above may also be realized in some other manner than that described above.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US5333175||Jan 28, 1993||Jul 26, 1994||Bell Communications Research, Inc.||Method and apparatus for dynamic power control in TDMA portable radio systems|
|US5839056||Aug 30, 1996||Nov 17, 1998||Nokia Telecommunications Oy||Method and apparatus for controlling transmission power of a radio transmitter|
|US5946346||Oct 7, 1997||Aug 31, 1999||Motorola, Inc.||Method and system for generating a power control command in a wireless communication system|
|US6215827||Mar 19, 1998||Apr 10, 2001||Lucent Technologies, Inc.||System and method for measuring channel quality information in a communication system|
|US6226526||Dec 18, 1998||May 1, 2001||Sony Corporation||Transmission power control method, base station apparatus and communication terminal|
|US6414946||Nov 17, 1998||Jul 2, 2002||Oki Electric Industry Co., Ltd.||Adaptive downlink transmission power control arbiter|
|US6529482||Jun 30, 1999||Mar 4, 2003||Qualcomm Inc.||Method and apparatus for adjusting a signal-to-interference threshold in a closed loop power control communications system|
|US20020080734||Nov 17, 1998||Jun 27, 2002||Shinichi Satou||Adaptive downlink transmission power control arbiter|
|US20020094836||Feb 8, 2002||Jul 18, 2002||Satoshi Nakamura||Transmission power control apparatus|
|US20020111163||Mar 26, 1999||Aug 15, 2002||Kojiro Hamabe||Method of preventing interference of adjacent frequencies in a cellular system by selection between adjacent carrier frequency and non-adjacent carrier frequency|
|CA2371315A1||Apr 19, 2000||Nov 2, 2000||Ericsson Telefon Ab L M||Power control in a cdma mobile communication system|
|EP0462952A1||May 22, 1991||Dec 27, 1991||Telefonaktiebolaget L M Ericsson||A method for regulating power in a digital mobile telephony system|
|EP0709973A1||Oct 24, 1995||May 1, 1996||Ntt Mobile Communications Network Inc.||Transmission power control scheme for mobile communication system|
|EP0853393A1||Jun 26, 1997||Jul 15, 1998||Ntt Mobile Communications Network Inc.||Transmitted power controller|
|EP0961417A2||May 26, 1999||Dec 1, 1999||Nec Corporation||Method for power control during call acquisition in cdma mobile communication systems|
|EP0963059A2||Jun 2, 1999||Dec 8, 1999||Nec Corporation||A CDMA mobile communication system and a transmission power control method for the same|
|JP2001136122A||Title not available|
|JPH11196042A||Title not available|
|JPH11234203A||Title not available|
|WO1997050197A1||Jun 26, 1997||Dec 31, 1997||Nippon Telegraph & Telephone||Transmitted power controller|
|U.S. Classification||455/522, 455/127.1|
|International Classification||G06F15/16, H04J13/00, H04B7/005, H04B7/26|
|Cooperative Classification||H04W52/36, H04W52/12, H04W52/24|